The way my mind works...
My brother once had 12" version of the Philips 1970's MFB's (Motional Feed Back, so the cone-movement of the woofer is measured and put back into the amplifier through some kind of processing).
The lows coming out of this were epic.

This led me to buy a relatively cheap set of active Sony MFB's. But even with MFB, a 6" is never going to sound like a 12"

So I am now stuck with a set of active bi-amped MFB ESL speakers (worth having just for the 6 words preceding this remark )

I knew the ESL's were not playing very well, so my question is either:

How do I restore the ESL's to their old glory? (Sony 1-504-680-11)

or

How does this SA-EX100 work and could I e.g. change the electrostats with some Elac 1" titanium tweeters I have lying around to at least have a cheap, but way better than average, computer speakerset?
Tried downloading the manual (from another, FREE site probably!) but this was only the first page (of which I did learn the amp is 50W for mid and 8W@50ohm for high. (I have a few 25W 45ohm resistors, serieswire to the 4ohm Elac and pray the efficiency is high enough for it to keep up with the mid?).

Thanks for any info/links/etc you can provide. (I know I can get the ESL's new for ~200 euro, but that's not the pricerange of repairs I was looking for...)

So I should have searched for an ERECTOstatic speaker... I Google translated it, but it was still hard to read. Maybe I'll mail him to see if he writes in English.

And I didn't buy them for the electrostats, I bought them because my love for (Philips) MFB's, the ESL's were just a bonus

That Tanya site is strange... I couldn't find the link and on the pic of the servicemanual they say the link is above the pic
I even failed the registering test, as I do not like to wire a 1W resistor to constantly dissipate 1.02W. At least I think that's the question I answered wrong...

Finally managed to download the PDF with the link that appears after a while NEXT to the pic. Helps a lot knowing the screws I couldn't find are behind the grill-attachement-holes!

I have some of these Sony speakers too, and they can sound really great!
Usually to fix the ESL tweeters you need to clean them and replace the foil.
The site mentioned in Japanese is about this, you can see how to disassemble the tweeters. I have obtained the best results with alumised 4 micrometer polyesther film. Once the tweeters reach their right output, you will appreciate these speakers for the great details in the high's, and the controlled low's.

Found a pic of the woofer?, as I thought from the manual it seems to use a separate feedback coil and magnetic circuit built into the driver, Long voice-coil former?
Very different to philips' implementation of MFB

Usually to fix the ESL tweeters you need to clean them and replace the foil.
The site mentioned in Japanese is about this, you can see how to disassemble the tweeters. I have obtained the best results with alumised 4 micrometer polyesther film.

The Japanese site: I couldn't work out if he was just talking about a sticky foil and solved it by taking it apart and rebuilding or that he indeed replaced the foil.

Where does one find this alumised polyester film? Are they ready made replacements or simply a roll of said material that you need to cut to size?

Yeah, the inner works of the tweeter is a sandwich of different components, glued together. This is the sticky part.. In the middle is a metal frame with the mylar foil glued to it, with a certain tension. This foil usually needs to be replaces because it has lost its conductivity. Sometimes just cleaning it does the trick. I used the aluminized mylar (polyester) foil from Mike Woodhouse - Free Flight Supplies
I see now that it has a thickness of 5 micrometer. I could send you a piece of the foil large enough to repair the tweeters, if you are planning on doing so, we live in the same country.

Is it hard? The "with a certain tension"-remark sounds like it will complicate things. For the rest it seems like a fun project that should be doable in a few hours. (Or am I greatly underestimating things here? )

Yes, with some basic skills and experience it should be doable in a few hours:
I used thin double-sided glue tape intended for glueing carpet to the floor to glue the foil to the metal frame. I first put the glue tape on all sides of the frame, then remove the protective paper. Try to obtain the same tension in the foil by comparing it to an unrepaired tweeter: by blowing in the assembled tweeter you can hear the foil resonate with its own frequency, which is an indication for the tension in the foil. If you glue one long side to the frame, and then with sslightly pulling on the foil glue the other sides to the frame, you can get some tension in the foil. Use a larger piece of foil, and after the glueing cut it neatly around the sides. Don't worry about the 6 mounting screw holes, when assembling the srews will puncture the foil without any harm. Just make sure you use the entire surface of the metal frame for gueing.
As far as I know the mylar foil has one side with the coating, and one side uncoated. I assumed that the most "shiny"side is the side with the coating. The uncoated side must be glued to the metal frame, so the the coated side (conducting) makes contact with the metal couterpart which is connected to on of the HV wires. This way the voltage is connected to the foil. You'll understand what I mean when you take the tweeter apart.
Good luck!

I see now that it has a thickness of 5 micrometer. I could send you a piece of the foil large enough to repair the tweeters, if you are planning on doing so, we live in the same country.

Just breaking in on an old conversation. I have a Sony Scala set with these SA-S1 speakers and they are great! Bought them myself in 1995. I recently acquired two additional SA-S1 speakers as part of a complete 2nd hand Scala set. Needed that bacause my own pre-amplifier TAE-S1 was defective and I wanted to have spares in abundance. Sadly, the tweeters of these two new speakers are defective, are completely silent. I would love to be able to restore them to their old glory and end with 4 of them

Do you still have a piece of the foil available? I would greatly appreciate it if we can arrange something.